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Specifications

DOI 10.1615/hedhme.a.000462

4.9 SPECIFICATIONS AND TENDERS
4.9.2 Specifications

What problems would occur if an inquiry were issued without a job specification and simply called up the applicable design code? After the purchase order was placed, the contractor would have to negotiate, typically, the price and delivery of spares, number of copies of drawings, guarantees, extent of supply, special tools and test equipment, and so on.

The code covers the detailed mechanical design methods to be used and refers to a large number of allowable materials of construction with their associated design stresses. It also details fabrication and inspection methods. The code requirements are legally mandatory in many countries.

A specification will add the contractor's and client’s technical requirements and clarify the code (or standard) when choices are available. It should contain a design and fabrication section based on experience in fabrication and problems in the field.

The specification, when accepted by the vendor, will be contractually binding. It will not deal with commercial considerations. Table 1 gives a list of items that should be included in most specifications. Table 2 lists typical requirements for shell-and-tube heat exchangers. Table 3 lists typical requirements for air-cooled heat exchangers. Table 4 lists typical requirements for plate and frame type heat exchangers. Table 5 considers a package unit (a cold box), which has much broader scope and requires liaison with other engineering disciplines. Table 6 lists typical requirements for electrical process heaters.

Table 1 Typical checklist common to most specifications

a Specify if after heat treatment; vendor may wish to do this before heat treatment only.
TopicComment
Scope of the specification


Summary of the specification content (design, materials, fabrication,
 inspection, testing, painting, preparation for shipment, and documentation).
Define the type of equipment.
Codes, standards, etc.
 Internal specifications
Comprehensive list of all relevant codes and standards with dales.

Vendor responsibilities
 Guarantees
For thermal design, mechanical design, fabrication, testing, painting,
 shipment as applicable.
Extent of supply
 Instruments
 Instrument connections
 Electrical and instrument cables
 Cooling water supply lines on package units, etc.
Important on package and skid-mounted units. Use diagrams to show what
 is supplied by vendor and what is supplied by others.



Documentation
 Design data
 Drawings
 Data report
 Certified material record report
 Weld procedures
 Certified (insurance) inspection
 Certificates
Specify which documents are required at tender (quotation) stage and
 which are needed after the order.
Vendor should supply a schedule of all drawings for the order with a full
 description of each drawing and latest issue date. This is very important
 on package units and should be maintained throughout the job.



DesignSee relevant equipment type.
Selection of materials
 Generic materials by contractor/client
 Allowable substitutes in various countries
 Clad or solid
Do not put onus on the supplier. Generally the supplier will put in the
 minimum-cost suitable material. Client/contractor should select materials
 based on experience and required life of the plant.

Fabrication
 Low-temperature requirements
 Hydrogen service requirements
 Clad plate
 Postweld heat treatment
Do not duplicate the code.
Clarify when alternatives are offered.



Inspection
 Radiography a
 Ultrasonic testing of plates a
 Magnetic particle a
 Dye penetrant inspection a
 Impact testing
Extent of nondestructive testing (NDT) should be defined at the tender
 (quotation) stage. After the order, vendor should supply an NDT map
 showing locations of ail inspection on a general arrangement drawing.



Testing
 Pressure tests, hydraulic/pneumatic
 Special leak tests
 Proof test
 Burst to failure tests



Brittle lacquer/strain gauge.
Generally for items not in the scope of the code.
Quality control


At the tender stage the vendor should submit a quality assurance manual
 and an inspection/test plan that includes a schedule of manufacture.
After receipt of order the vendor should prepare a detailed quality plan.

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